© 2007 Ideal Industries 1 of 56 Basics of Branch Circuit Testing Branch Circuit Testing

Basics of Branch Circuit Testing© 2007 Ideal Industries www.idealindustries.com 1 of 56

Branch Circuit Testing



• Why test branch circuits

• Causes of branch circuit failures

• Emerging Technologies

• General Tests methods

• Type of Testers.


Why Test Branch Circuits?

Safety Issues• Electrocution• Equipment failure• Fire caused by

Electrical circuits– Branch Circuits with

or without AFCI protection


Electrical Shock

• 490 people lost their life from Electrocution in 1997* from:– Consumer products – 24%– Large appliances - 16%– Installed home wiring - 12%

*NFPA and US Consumer Product Safety Commission 1997 data

Every week someone is killed by Electrocution through installed home wiring.


Causes of Electrical Shock

• There have been several changes to UL943 Requirement for GFCI’s due to studies over several years of older units not operating properly.

• Effective January 2003• www.ul.com/media/newsrel/nr072302

– Defective wiring, Neutral to Ground bonds.– Poor Ground conductor circuit– Poor Earth Ground

Defective protection devices like TVSS, and GFCI


Equipment Failures

Failures result in:• Erratic operation• Lost productivity• Lost/corrupt data• Damaged equipment• Poor power efficiency


Fires

– 406,000 residential structural fires• Residential fires accounted for 74% of all structure

fires– 3,390 civilian deaths and 17,775 injuries

• Residential fires resulted in 97% of all deaths and 87% of injuries

– 9% of all structural fires and 7% of deaths were a result of failures within the electrical distribution system

www.cpsc.gov/library/fire97.pdf

NFPA and US Consumer Product Safety Commission 1997 data showed


Estimated Fire losses

Electrical Distribution

Fires Injuries Deaths

Installed Wiring

14,600 420 110

Cord, Plug 6,300 320 90

Switch, Outlet 4,900 160 10

Lamp, light Fix.

9,900 350 30

Other 4,600 10 10

Total 40,300 1360 250

*NFPA and US Consumer Product Safety Commission 1997 data


Estimated Fire losses

• According to a recent report by the National Association of State Fire Marshals, during the period from 1994-1998, there was an average of over 70,000 total electrical fires, which were responsible for over 500 deaths

• Of these 70,000 electrical fires, 60,000 were caused by arcing, not from an overloaded or short circuit

"AFCI Inquiry and Report" by the Consumer Product Safety Task Force of the National Association of State Fire Marshals, August 1, 2002.


Causes of Electrical Fires

• Series Arcing Faults: can be Defined as a partial or total conductor or path in series with the load that alternates between infinite resistance to high resistance or normal. – Since the arc condition is in series with the load, the arc

current cannot exceed the loads current.

– Series arcs may contribute to insulation degradation that might lead to parallel arc conditions.

• Example would be a break in the conductor which has carbonized or has intermittent contact.

Arc-fault Circuit Interrupters--A Critical NEC 2005 Issue / High Resistance Series Fault 4 Brendan Foley, Joseph Engel, and Clive Kimblin.



• Parallel Arcing Faults, occur as a short circuit or a ground fault. – A short circuit arc decreases the dielectric strength of

insulation separating the conductors, allowing a high-impedance, low-current arc fault to develop, that carbonizes the conductor's insulation, further decreasing the dielectric of the insulation separating the conductors.

– The result is increased current, exponentially increased thermal energy, and the likelihood of a fire. The current flow in a short circuit, parallel arc fault is limited by the system impedance and the impedance of the arc fault itself. Not necessarily the breakers rating.

The Basics of Arc-Fault Protectionby Mike Holt, Mike Holt Enterprises, Inc. | Apr 01 '02 EC&M



• High Resistance Fault: is a series fault characterized by the presence of abnormally high resistance, compared to a normal wire, wire termination, or wire splice, resulting in a reduction of capacity and heat dissipation at the fault. – These high resistance series faults result from a build-up of copper or

aluminum oxide that creates a high resistance, "glowing contact.“ – This high-resistance point can become extremely hot with

temperatures exceeding 600° F causing insulation failure, that can result in a damaging high-power parallel arcing fault or ground fault.

– Glowing contacts can develop at virtually any electrical connection conducting current. The current in the high resistance fault, like the series arcing fault, is limited to the current being drawn by the load—until the insulation degrades to the point where this type of fault becomes a parallel arcing fault or causes leakage current to ground.

Arc-fault Circuit Interrupters--A Critical NEC 2005 Issue / High Resistance Series Fault 4

Brendan Foley, Joseph Engel, and Clive Kimblin.



• Summary, Series or High Resistance Arc Faults: are the results of defects in the wiring as part of a conductor or connection that is in series with the load Since the arc condition is in series with the load the arc current cannot exceed the Loads current.

– Glowing contacts in copper or aluminum wiring– High resistance in Back-wired devices like

receptacles – Loose or corroded connections– Bad splices– Hot plugs, or high resistance contact between outlet to

plug.


New Technology

• AFCI breakers were adopted in the NEC 210.12 defined as a device to provide protection from an ARCing Fault.

• UL 1699 Defines the requirements for these devices, but the most common and commercially available is the Branch/Feeder or B/F type. – In there are discussion that for

2008 a combination AFCI breaker will be adopted. This breaker would sense both Series and Parallel faults.


New Technology

• AFCI B/F breakers sense common load current and adds protections from parallel arcing faults and Ground faults

• UL and EIA determined that protection from a Series arc that included arcing to ground be at least 5 amps

• They also reported that the lowest short circuit current line-neutral in the US to bewithin 75 amps at a receptacle. All currently available AFCIs

will detect line-to-ground arcs at 50mA or above


New Technology

• What does a Branch/Feeder AFCI do.– Over current protection: This is the normal function of a breaker. To trip

when the load current has exceed the current rating of the breaker. – Hazardous Arcing: An AFCI will trip when it senses a characteristic

arcing between line and neutral above 75 amperes. – Ground Faults: The standard requirement for an AFCI is to trip on a line

to ground fault of 5 amperes or greater. Most AFCI will trip between 30mA to 50mA.

– Neutral to Ground Faults: If the neutral conductor comes in contact with a grounded circuit the AFCI will trip.

UL 1699 defined six devices, but three major types of AFCI's for branch circuits, Branch/Feeder, Outlet Circuit, and Combination devices. The Branch/Feeder type is the most common and the only device at this time that satisfies the current NEC requirements.


New Technology

* Part of Table 1 from The Truth About AFCIs (Part 1)

Table of ARC Detection and Protection Capability From A Branch Feeder AFCI

Arc Condition Branch/Feeder type

Line-to-Neutral Yes- 75 A

Line-ground Yes- 50 mA

Series with ground Yes - 5 A

Series without gnd no


Testing of the Branch Circuit

• General Testers cannot identify High Resistance or Series faults nor can they identify a Neutral to ground bond– Glowing contacts in copper or

aluminum wiring– High resistance in Back-wired

devices like receptacle – Loose or corroded connections– Bad splices– Hot plugs, or high resistance

contact between outlet to plug.

A high resistance connection, can result in

hot spots or Glowing connections which can

breakdown in insulation and poor efficiency of the

electrical system



• Nor can a General Tester identify a “False” or “bootleg” ground– Defined as an accidental short or improper bonding

of ground to neutral conductors

– Shows up as normally wired condition with general receptacle testers

– Sensed by the new AFCI breakers, Conditions will trip an AFCI at turn on.

• At times may be very difficult to locate.



• Before the adoption of the AFCI Circuit breaker, Many of the same wiring faults existed and still exist today in standard branch circuits,

– BUT DO WE TEST FOR THEM ON NON-AFCI CIRCUITS?

• AFCI’s have helped minimize wiring or load defects in the branch circuits with which they are associated, but it doesn’t address all circuits.

• Series faults are not covered by the present AFCI technology.

• Is there a way to Identify many of the problems found in branch circuits today?



• Measure the voltage drop at the furthest receptacle from the panel

• Low voltage drop indicates a low impedance system

– Lowers the risk of hidden hazards

– Improves power efficiency and operation

NEC code Articles {210-19(a) FPN No. 4} {215-2(d) FPN No. 2} - “Branch circuit conductors should be sized so as not to exceed a maximum voltage drop of 3% at the farthest outlet , and that the combined voltage drop for both a branch and feeder should not exceed 5%”

Using Voltage Drop



– Undersized wiring for load or length of run• NEC 210-19(a) FPN no.4 states that conductors be sized to

provide reasonable efficiency of equipment operation– High resistance connections

• Loose or corroded connections• Poor splices• Defective devices

• Voltage drop can detect an estimated 90% of defects on a branch circuit

Testing under a load and calculating voltage drop can identify common wiring problems



• Lets do a little Experiment to test this out. I have a circuit with a receptacle at the end of 60 feet of wire– With no-load is the voltage

the same on DMM A and DMM B?

– Note reading– With a load attached to the

circuit is the Voltage the same on DMM A and DMM B ?

– Note reading• Calculate Voltage drop

Voltage Drop = V (no-load) – V (load)

% Voltage Drop = Voltage Drop/ V (no-load)



• A hair-dryer or drill worked well as a load for this test

• We Measured the line voltage with no-load and then with load and recorded the reading

• If a circuit was already under a load the additional 10-12 amp load would trip the breaker

We all remember the Old Way



• A Device like the IDEAL SureTest circuit analyzer places a load on the line and Calculates the 12, 15, and 20 ampere voltage drop. – One method to Identifying

High resistance circuit faults• Patented technology pulses the

load on the line without tripping circuit breakers or interrupting existing equipment

Using Modern Technology


• VD = I x R

– I = Current = 16 Amperes

– R = Resistance of conductors = .4 Ohms

• 2 Ohms/1000 feet for 12 gauge (Chapter 9, Table 8)

• 2 Conductors of 100 ft = 200 Feet

• (2/1000) x 200 = 0.4 Ohms

• VD = 16 A x 0.4 = 6.4 Volts

• VD% = 6.4/120 = .05333 or 5.3


Calculating Voltage Drop



• Using this method not only helps us determine the integrity of the circuit, it also gives additional information, not just the resistance of the conductors, but of the entire circuit.



• Measure the voltage drop at the furthest receptacle from the panel and record the reading

• Repeat this at each receptacle until you find a significant decrease in voltage drop from one receptacle to the next– At that point check the circuit and wiring leading to the last

receptacle.

• Check voltage drop on remaining receptacles– If voltage drop is acceptable in remaining receptacles, then the

problem is probably localized at the receptacle connection– If voltage drop is unacceptable, then the problem exists within

the hot or neutral conductors

Finding the Cause of High Impedance



If all devices have high voltage drop then the high impedance is caused by:– Undersized wire for length of run– Splice between the panel and the first device– Poor connections or corroded contacts at

panel, breaker, neutral bus, etc.




In this example there is a poor connection between Device 2 and 3 which did not show up with a DMM reading. Under a load test the voltage drop on device 3 and 4 was 12%. The voltage drop at device 2 decreased to 8%.




• SureTest also shows correct wiring including Identifying Neutral to ground contact faults to within 15’ of the fault and 15’ from the panel.

• Conductor impedance of Hot, Neutral and ground

• N-G Voltage • GFCI With time to trip• ARCI Fault testing



• Most poor panel connections show up as hot spots in the panel– Test quickly with an infrared

temperature meter

• Voltage drop across contact point, such as a breaker should not exceed 10mV to 100mV. This is also true for switch contacts. – Check contact points and breaker

Finding Hot Spots



Three major reasons for ground • To provide Zero reference for the electrical

service• Provide a low resistance path to protect from

electrical faults• Protect equipment against static electricity and

protect against frame potential for the operator’s safety

Importance of the Ground wire



• High impedance grounds

– Rule of thumb < 1 Ohm

– Electronic equipment and data networks require very low impedance

• IEEE recommends < 0.25 Ohms

• False Grounds

• Undersized ground conductor, corroded or loose contacts

– If circuit conductors are increased in size to accommodate voltage drop the ground should also be sized accordingly (NEC –122(b)

Common Faults with the Ground wire

The SureTest Patient Technology can test the Impedance The ground wire and also Identify false or N-G faults


Installation of Safety Devices

• Ground Fault Circuit Interrupters– NEC requires installation of

GFCI in bathroom, kitchens and outside.

– Purpose is to protect individuals by detecting ground faults.

– Defective or improperly installed GFCI can lead to shock. SureTest family have GFCI testing,

some provide in the testCurrent and time to trip information


Ground Electrode

• NEC Code 250-56 requires a single ground electrode to have 25 Ohms or less resistance, and if not, be augmented by one additional rod spaced at least 6’ apart of any type specified in section 250-50 or 250-52

• This measurement can be taken with a three point earth resistance tester or a ground resistance clamp meter


Integrity of the Branch Circuit

• Over-current. For any current above its current rating it will trip according to its circuit breaker time-current characteristic.

• Hazardous arcing. For arcing at current levels of about 75 amperes and above, the AFCI will trip. Commercially available AFCIs will actually operate at some level below 75 amperes. The AFCI will operate faster than a fuse or circuit breaker under short-circuit over-current conditions up to about 125 amperes.

• Arcing ground faults. The standard requires tripping on faults of 5 amperes and greater. Commercial units will actually detect ground faults of 50 milli-amperes and greater. Tripping will be instantaneous, with no intentional delay.

Causes of AFCI Tripping at turn on



Shared Neutrals is a practice where one three wire conductor is used as a homerun for two single-phase circuits.

Shared Neutral in residential wiring t



• Neutral grounding. If the neutral conductor (grounded-circuit conductor) of an AFCI protected circuit touches the ground wire or grounded metal, the AFCI will trip, if the impedance to ground is very low impedance.

• Abnormal environments. Some abnormal events may also cause tripping, such as high voltage surges from lightning or utility line surges, voltage or frequency fluctuations from poorly regulated backup generators, or mechanical shock.

Causes of Tripping at breaker turn on or with load



• If after Energized, an AFCI circuit immediately trips, what steps should be taken?

• Well , a lot of approaches have been suggested , but an orderly search or approach will help reduce the stress.

• Remember that AFCI’s have two primary Functions– Over-Current sensing – Arc Fault condition

• One of the most common faults is found to be a * Neutral to ground contact fault or false ground.

* The SureTest Patient Technology can test the Impedance of the ground wire and also Identify false or N-G faults

Finding the Causes for the Trip



• The AFCI will sense an arc that occurs because of Insulation or isolation break-down, which can be tested with an insulation tester– Disconnect all loads and verify that unconnected wire ends

are insulated. – Disconnect the load wire to the AFCI, or GFCI in the

circuit. Use the Megger to apply a direct voltage starting with 250 then 500.

• It is always best to start with a voltage that is 2X the rating of the source and increase if necessary

• A rule of thumb is, roughly 1 megohms per 1000V, but it is always best to consult with the wire manufacturers for best results.




• If the trip is not Instantaneous, it would indicate an overload trip

• Energize the circuit and measure the load current over time. A clamp meter should be able to determine this.

– A DMM with CT that has a fast Peak hold function, may also be useful in Identifying between Over-Current and Arcing.

– Disconnect load and reinstall to Identify the defective device.





• If the trip is Instantaneous, it could indicate Ground Faults or earth leakage.

• Ground faults are small amounts of current that “leak” over to ground caused by deteriorating insulation or moisture. – A Low amperage current clamp or clamp meter, with a low range

having the ability to measure 5-10 mA accurately, could help.• The GFCI or AFIC measure the difference between current out

and current in. If there is an imbalance, it will trip. • Disconnect load and reinstall to Identify the defective device.




• Verify that electrical devices have been wired up correctly

• Maintain a low impedance electrical system

• Maintain a good electrical ground

Protect personnel and equipment by:



• Not all Testers are what they seem to be!• Branch circuit testing should

– Verify proper wiring– Measure the integrity of the branch circuit– Measure the integrity of the ground conductor

• Measure the integrity of the ground electrode• Install and test the operation of safety devices

Use certified devices and testing equipment



• Certification labs test devices and equipment for failure under extreme conditions to protect consumers

• With “Free trade and open markets” there has been an surge of counterfeited certifications

• UL provides information on their web site

www.ul.com/retail/certified.html


Receptacle Testers

• Check to ensure that devices have been wired up correctly immediately after installation– Proper wiring of receptacle– Correct voltage level– Good continuity on

switches – Warn against faulty wiring

in 3-wire receptacles

• Test GFCI receptacles for proper operation



• To test a GFCI, an imbalance needs to be placed between hot and neutral

• The the amount of imbalance and time to trip should be monitored to verify GFCI performance

• Many receptacle testers will test GFCI receptacles

• The Ideal 61-058 will not only test GFCI but will also test the AFCI Breaker


Circuit Identifiers

• Identify circuit breakers and fuses without service interruption

• Automatic or adjustable sensitivity levels

• Visual and audible indication

61-532 model has an Analog Receiver

61-534 has Digital Receiver w/ NCV, High voltage transmitter with GFCI


Voltage/Continuity Testers

• Test from ranges of 6-600V volts AC or DC

• Some units vibrate to provide tactile indication of voltage level

• Audible continuity



• To test a AFCI you need to generate a number of high current pulses to simulate the effect of an arc condition that may exist in wiring or cords,

• IDEAL has Two Testers which can simulate an arc

• They Are the; – 61-058 GFCI/AFCI testers– 61-165 Circuit Analyzer

with AFCI and GFCI


SureTest Circuit Analyzer

• Measures integrity of a branch circuit– Voltage drop under an actual

12, 15, 20 Amp load• Measures Conductor and ground

impedance• Wiring and Identifies false

grounds• GFCI • AFCI• Some models not shown Measure

harmonic distortion

61-164

SureTest

Circuit Analyzer

61-165 SureTest Circuit

Analyzer with AFCI


Infrared Temperature Meter

• Checks for hot spots in breakers and panels• Laser point sighting to target device under

test• 15 to 1 angle of view ability

– 15 inches from panel will measure temperature across 1 inch circle


Earth Testers

• Ideal/Megger 61-788 – 3 pole Testers

• IDEAL/Megger 61-789– 4 pole Testers– Self powered - no need for

hand crank– Low power consumption

Compact and lightweight– Quick battery check– Limited lifetime warranty


Earth Testers

• Ideal 61-920 Ground Resistance Clamp – Ground Resistance

– Ground Leakage Current

– Auto ranging

– Audible indication < 40 ohms

– Open jaw indication

– Data hold

Documents

© 2007 Ideal Industries 1 of 56 Basics of Branch Circuit Testing Branch Circuit Testing